"The scent molecules produced by flowers in a less polluted environment, such as in the 1800s, could travel for roughly 1,000 to 1,200 meters [3,300 to 4,000 feet]; but in today's polluted environment downwind of major cities, they may travel only 200 to 300 meters [650 to 980 feet]," said study team member Jose D. Fuentes.

With flowers no longer advertising their presence over as large an area, pollinators are forced to search farther and longer to pick up the hint of their scent. They may also have to rely more on their sight than what they smell.

Bees depend on flower nectar for food, and if they have a hard time finding the flowers, they can't sustain their populations.

Other studies, along with the experiences of farmers, have indicated that bee populations are dropping in places such as California and the Netherlands. Fuentes and his team think air pollution may be the reason.

The research, funded by the National Science Foundation, is detailed online in the journal Atmospheric Environment.